There are large magnetic fields developed around, among others, power equipments or power lines, such as in power plants or substations. In such power plants, substations, or the like, making use of an electric signal for precise measurement of voltage or current sometimes leads to a failure due to influences of surrounding magnetic fields. To this point, there have since ever been techniques for measurements of voltage or current by use of an optical signal free of influences of magnetic fields (ex. refer to patent document 1).
There will be brief on an apparatus adapted for optical measurement of voltage (optical voltage measuring apparatus) with reference to FIG. 1. FIG. 1 illustrates an optical voltage measuring apparatus 2, which includes a light source driver 11 under control to have a light source 12 emit flux of light, which is conducted through an optical fiber 13a to a light sending collimator 14. The light sending collimator 14 changes incoming light from the optical fiber 13a into parallel light, to send to a polarizer 15. At the polarizer 15, incoming light from the light sending collimator 14 is linear polarized, and at a retardation plate 16, linear polarized light from the polarizer 15 is circular polarized, to provide reference light. There is a voltage imposed as a target of measurement on an electro-optical device 17. The electro-optical device 17 is configured to polarize incoming light from the retardation film 16, in accordance with an electro-optical effect due to the imposed voltage 17a. Polarized light from the electro-optical device 17 is received by an analyzer 18, and a light receiving collimator 19 changes incoming light from the analyzer 18 into parallel light, to conduct through an optical fiber 13b. This involves an optical signal to be detected through the optical fiber 13b, which is converted by a detector 21 into an electric signal. Afterwards, the electric signal after conversion by the detector 21 is processed by a voltage measurer 22 for calculation of the voltage to be measured.
In order for the optical voltage measuring apparatus 2 to implement measurements with high precision, the polarizer 15, retardation plate 16, electro-optical device 17, and analyzer 18 should have stable polarized light. However, the devices 15-18 have photoelastic effects due to vibrations, the photoelastic effects disturbing polarized status. On the other hand, as an object of voltage measurement by the optical voltage measuring apparatus 2, the power equipment or the like may be high voltage equipment that may undergo large vibrations in an environment in which the optical voltage measuring apparatus 2 would be installed. For instance, the high voltage equipment has a breaker for current interruption upon occurrence of anomaly, the breaker being set to turn on and off, producing vibrations exceeding 1,000 G. The optical voltage measuring apparatus 2 might have been installed under a condition that would produce such large vibrations, constituting a difficulty to provide a stable polarized status.
There has been a known anti-vibratory measure including, as illustrated in FIG. 1, the devices 14 to 19 arranged on a base plate 25, with an elastic body in between, the elastic body absorbing vibrations to prevent the devices from being vibrated.
Referring now to FIGS. 2 to 4, there will be described an adhesion method of the electro-optical device 17, together with problems due to vibrations. The description addresses a case of the electro-optical device 17, while the other devices 14 to 16, 18, and 19 also are each adhesive bonded to the base plate 25 in a similar manner, with a similar problem.
As illustrated in FIG. 2(a), the electro-optical device 17 is adhesion-bonded through an elastic body 23 onto the base plate 25. In a state of the base plate 25 being given no external vibrations, as illustrated in FIG. 2(a), the electro-optical device 17 is kept parallel to the base plate 25. On the other hand, if the base plate 25 is given a vibration, as illustrated in FIG. 2(b), the electro-optical device 17 is caused to incline relative to the base plate 25, by inertial forces acting on the electro-optical device 17.
In the state given no vibrations, as illustrated in FIG. 3(a), the electro-optical device 17 has an attitude perpendicular to an optical axis L. When the electro-optical device 17 is in the attitude perpendicular to the optical axis L, outgoing light travels, striking into an opening 19a of the light receiving collimator 19 in a prescribed position, so the light receiving collimator 19 is adapted for detection of light.
On the other hand, if given an external vibration, the electro-optical device 17 has an inclination, and as illustrated in FIG. 3(b), the electro-optical device 17 has an angular deviation. That is, there is an angular deviation δ developed between an optical axis L1 of incoming light and an optical axis L2 of outgoing light, so outgoing light is unable to strike into the opening 19a. Hence, the light receiving collimator 19 fails in detection of light, as a problem. Such a failure in detection of light at the light receiving collimator 19 makes it unclear to determine if the failure in detection of light is derived from a polarization of light by a voltage to be measured, or if the failure in detection of light is derived from any angular deviation by vibration at a device such as the electro-optical device 17, with a resultant failure in voltage measurement to be accurate.
Such being the case, in regard of the electro-optical device 17's inclination due to vibration, the degree became greater as the adhesive 23 had an increased thickness, as a problem. Therefore, the adhesive 23 of an elastic body used as an anti-vibratory measure would be warped, causing an angular deviation of the electro-optical device 17, as a problem.
FIG. 4(a) illustrates a state being free of vibrations, like that in FIG. 3(a). In FIG. 4(b), the electro-optical device 17 is given an external vibration, and displaced from the state, making a translational movement, where it is allowed to hold an attitude perpendicular to the optical axis L. Therefore, if the electro-optical device 17 is displaced by a transitional movement due to vibration as illustrated in FIG. 4(b), then flux of light passing through the electro-optical device 17 can strike into the opening placed in the prescribed position, to be detected by a device in a subsequent stage, thus allowing for an accurate voltage measurement in the optical voltage measuring apparatus 2.
As described, given vibrations to devices 14-19, the optical voltage measuring apparatus 2 might suffer from an optical axis deviation as a hindrance against accurate voltage measurements, while it might have devices 14-19 displaced by a translational movement, where it would hardly be affected by vibrations, as a characteristic point.
However, for the method of adhesion bonding the devices 14 to 19 by the adhesive 23 onto the base plate 25 being flat in shape, it was difficult to predict in which directions the devices 14 to 19 would move, so it was disabled to control moving directions. Accordingly, for instance, for provision of an anti-vibratory measure including the devices 14 to 19 adhesion-bonded onto the base plate 25, enabled was no more than suppressing the thickness of adhesive 23 to a minimized permissible thickness to keep the devices 14 to 19 from being inclined by vibration, thus failing to implement a sufficient anti-vibratory measure, as a problem.